Micromachined (MEMS) gyroscopes have become established as useful commercial items. Generally speaking, a MEMS gyroscope incorporates two high-performing MEMS devices, specifically a self-tuned resonator in the drive axis and a micro-acceleration sensor in the sensing axis. Gyroscope performance is very sensitive to such things as manufacturing variations, errors in packaging, driving, linear acceleration, and temperature, among other things. Basic principles of operation of angular-rate sensing gyroscopes are well understood.
Conventionally, bulk acoustic wave (BAW) MEMS gyroscopes operate based on utilizing a pair of orthogonal modes to sense rotation. One of these modes is driven into self-sustained mechanical oscillations. When the sensor experiences external rotation, energy couples from the driven mode of vibration to the orthogonal mode via the Coriolis force. Sensing the energy coupled into the orthogonal mode forms the principle of operation of such MEMS gyroscopes.
Electrostatically actuated BAW gyroscopes typically utilize narrow air gaps (approximately around a few hundred nanometers) to efficiently actuate high frequency mechanical modes. Operating with small gaps makes the system vulnerable to any small changes in gap (for e.g. 5nm change in 100 nm gap corresponds to 5% change, as compared to 0.5% in 1 um gap). Changes in gaps amount to changes in sensitivity (scale factor) and zero-rate offset for these gyroscopes.